The keyboard, or clavier, has for centuries been an input device for musical instruments. Until the late 19th century, keyboard instruments actions were purely mechanical, as they remain today in most pianos and in tracker organs. In the late 19th and early 20th centuries, pneumatics were applied to organ actions. Shortly thereafter, electro-mechanical actions were applied to organs, and are still often employed, either alone, or combined with pneumatic devices. After the first quarter of the 20th century, electrical and electronic organs were developed, which are controlled by electrical switches.
Electrical contact key switches are subject to unreliable operation, due largely to corrosion, dirt, and metal-fatigue. One may still purchase key contact blocks for early electro-pneumatic organs comprising several resilient wires embedded in a wooden block. Despite contact redundancy such malfunctions as dead notes and “ciphers” (notes stuck on) are common with such switches, and sometimes disrupt organ concerts.
Numerous and varied non-contact electrical keyboard switches have been devised. In U.S. Pat. No. 2,873,637, Herold teaches a capacitive touch control keyboard, as do Jones in U.S. Pat. No. 3,507,970, Cockerell in U.S. Pat. No. 3,836,909, Nagai et al. In U.S. Pat. No. 3,943,812, and Moog in U.S. Pat. No. 4,213,367. Potzl teaches a gas-discharge device in U.S. Pat. No. 3,002,411. In U.S. Pat. No. 3,248,470, Markowitz et al. Teach detection by voltage induced into a coil by a moving magnet, as do Ohno in U.S. Pat. No. 3,708,605, Yamamoto et al. In U.S. Pat. No. 4,524,669 and Muramatsu in U.S. Pat. No. 5,107,748. In U.S. Pat. No. 3,313,877, Boenning teaches using a linear variable displacement transformer (LVDT) as a key input detector. In U.S. Pat. No. 3,255,293, Walker teaches the use of a saturable transformer for key detection, as does Michel in U.S. Pat. No. 3,353,030. In U.S. Pat. No. 3,590,134, Ogi teaches the use of a magnet and magneto-resistor as a key detector, as does Ohno in U.S. Pat. Nos. 3,594,488 and 3,617,600. Jones, in U.S. Pat. No. 3,594,487, teaches moving a metal object to modify the coupling of a transformer as a key detector, as does Kishi in U.S. Pat. No. 3,805,185. Klann, in U.S. Pat. No. 4,151,174, teaches the use of a reed switch, a hermetically-sealed magnetically-operated electrical contact, in an organ pedal board. In U.S. Pat. No. 4,362,934, McLey teaches the use of an opto-electric device as a key detector, as do Tamaki in U.S. Pat. No. 4,974,482, Miller in U.S. Pat. No. 5,237,123, Vandervoort in U.S. Pat. No. 5,505,115, and Kimble in U.S. Pat. No. 5,567,902. In U.S. Pat. No. 4,366,463, Barker teaches the use of a Hall-effect device and a magnet as a key detector, as does Lee in U.S. Pat. Nos. 6,384,305 and 6,472,589. In U.S. Pat. No. 4,425,511, Brosh teaches a key detector based on geometric change modifying transformer coupling. In U.S. Pat. No. 4,838,139, Fiori uses a movable metal spoiler to alter the inductance of a coil to change the resonant frequency of an LC tank circuit as a key detector, as does Muramatsu in U.S. Pat. No. 5,187,315. The use of a piezoelectric element as a key detector is taught by Fields in U.S. Pat. No. 5,237,125.
The plethora of largely non-contact key switches cited above underlines the basic problem that electrical-contact switches may be effective and reliable in heavy-duty applications where sufficient voltage or sufficient mechanical force may be applied to effect adequate contact, but are problematic for delicate switching tasks. Most non-contact switches rely upon a field or a wave that can generate a detectable electrical effect. The electrostatic field underlying capacitance detectors incurs a fundamental limitation. Materials of a wide variety of dielectric constants and conductivities that interact with electrostatic fields are ubiquitous. Electro-optical devices are more controllable, but their widespread use has only recently become practical. Since most common materials are not significantly magnetically permeable, magnetically operated switches have historically been the most controllable type. Therefore, magnetically controlled switches dominate the devices cited above.
Magnetically operated switches have been employed for data entry key switches, for proximity detectors, and in electrically operated security and munitions systems. In U.S. Pat. No. 3,531,792, Bagno et al. Teach an “alarm system using saturable contacts.” In U.S. Pat. No. 3,921,530 Burkhardt et al. Teach a similar method fitted to a trip wire for intrusion detection and activating munitions. In U.S. Pat. Nos. 3,612,241, 3,368,221, 3,368,222, 3,698,531, and 4,099,176 Bernin et al. Teach a variety of magnetically operated key-switches, as do Madland et al. in U.S. Pat. Nos. 3,714,611 and 4,028,696, Wnantowicz in U.S. Pat. No. 4,017,850, and Sidor in U.S. Pat. No. 4,137,512. These magnetically operated contact-less devices may be classified as flux-gate switches which depend on the saturation or de-saturation of the core of an inductor, or of a transformer, to change the inductive reactance, or the coupling, respectively, of the same. All require a AC source of excitation to be applied to the inductor and detection circuitry to sense the inductive or coupling change caused by saturation or de-saturation of the core. Some are mechanically complex, electrically complex, or both.
The two most practical prior art magnetic switches are the Hall-effect switch and the reed switch, both of which share a common deficiency for organ console use. Most economical Hall switches toggle at less than 100 Gauss field strength. Most reed switches, though somewhat less sensitive, are designed to operate with minimum field strength to conserve power in such applications as relays, and to maximize sensitivity in intrusion detection apparatus. This sensitivity can be a problem in organs consoles where a row of registration controlling stop action magnets, known as SAM's, resides directly above the upper manual. Most SAM's have poorly configured magnetic circuits and leak magnetic flux of hundreds of Gauss at distances of a few inches. SAM's are well-known to leak flux badly enough to interfere magnetically with each other. Employing magnetically sensitive switches in the vicinity of SAM's may invite unwelcome organ noises when organ registration is changed.